I could drive the car would use the conditional of potere - Potrei guidare l'automobile .Could in the past tense is potevo as Paul said but that sentence doesn't work in the past tense.
Try I could hear the bells - Potevo sentire le campane.
Che ne dite?
Yes I think u can translate both with "I could". The difference more than the tense I think that is a question of ability against will. However we prefer potuto(past participle) for negative forms(or almost negative such as "ho potuto SOLTANTO/... SOLO...", here are some examples:
e.g.: 1a)potevo fare di meglio > I could do it better (I was able but I didn't: I didn't give all my efforts for that or I did't want to)
1b)non ho potuto fare di meglio> I couldn't do it better ( I've tried but I wasn't able)
2a) potevo leggere anche tutto il libro> I could even read the whole book in once (I was able but I did't)
2)ho potuto leggere solo tre pagine perche' nn ho avuto molto tempo. > I could read just 3 pages because I didn't have much time(=I wasn't able to read more than 3 pag.)
HOPE THAT COULD BE USEFUL...
Yes, I can imagine how it sounds. I just hoped it'd help clarify.btw "I wasn't being able to study" I dont believe is correct in English and it's not how I would say it. Just take out the 'being' and it sounds more natural to me. however I think if you were to use "I was being" you'd need an adjective afterward like "I was being good for her" But I don't believe this is said too often if at all.